A toxicology testing is the search by the laboratory of the possible etiologic agents that can cause poisoning. Given the wide variety of substances that can poison a person, the laboratories should work coordinated with the emergency wards in order to determine the appropriate tests menu and the required turn around time according to the most frequent causes of intoxication in the local population. Toxicology laboratories should provide two tiers of drug testing: selected drug tests in blood/urine and comprehensive or broad-spectrum toxicological testing in the same or other samples. The medical order must always include the suspected diagnosis, which is responsibility of the physician requesting the test. A most important issue in the study of a poisoned patient is the opportunity when the samples are drawn, which should be at the emergency room since a delay in sample collection implies losing unrecoverable information. Samples should be sent to the laboratory for either immediate analysis or later comprehensive toxicological tests, so that laboratories must have procedures for the proper storage and preservation of samples. Poison control centers provide assistance to clinicians in considering certain drugs etiologies and in selecting specific tests.